511 lines
8.1 KiB
ArmAsm
511 lines
8.1 KiB
ArmAsm
;---------------------------------------
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; based on 1bir - 1 block interactive raycaster for Commodore 64
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; coded by huseyin kilic (wisdom) copyright (c) 2009-2013 crescent
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;
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; converted to Apple II by Vince `deater` Weaver
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.include "hardware.inc"
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; zero page
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V2 = $2D
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COLOR = $30
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RAYPOSX = $61
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RAYPOSXH = $62
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RAYPOSY = $63
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RAYPOSYH = $64
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STEPX = $66 ; leave 1 byte between x and y
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STEPY = $68
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PLAYERX = $69
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PLAYERXH = $6a
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PLAYERY = $6b
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PLAYERYH = $6c
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DISTANCEL = $6F
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DISTANCE = $70
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NEWLOC = $71
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HEIGHT = $73
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HEIGHTL = $74
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ROWPTR = $d1
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ROWPTRH = $d2
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LINEH_T = $d9
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WALL_HEIGHT = $f8
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FLOOR_SKY_HEIGHT= $f9
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; external value dependencies
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HEADING = $81
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SINADD = $9a
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COLORS = $b1 ; 3 bytes consecutively
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; constants
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sin_t = $1000
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blocksize = $28
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cosine_table = $F5BA
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;---------------------------------------
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; main
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;---------------------------------------
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main:
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jsr SETGR
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; lda #$20
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sta HEADING
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;---------------------------------------
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; sin/cos table generator
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;---------------------------------------
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; first generate sine for 0..63 (0..90 degrees)
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; lda #3
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; sta SINADD
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; lda #$00
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; tay
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;gensin_loop:
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; sta sin_t,Y
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; iny
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; clc
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; adc SINADD
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; ldx SINADD
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; dec sincount_t,X
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; bne gensin_loop
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; dec SINADD
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; bpl gensin_loop
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; x = $00
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; y = $40
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; next generate
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ldx #$00
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ldy #$0f
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lda #$0
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gensin_loop2:
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lsr
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sta sin_t+$10+1,Y ; store 90-180 degrees
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sta sin_t,X ; store 0-90 degrees
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sta sin_t+$40,X ; copy at $40 so cosine is easier
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eor #$ff ; invert
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sta sin_t+$30+1,Y ; store for 270-360 degrees
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sta sin_t+$20,X ; store for 180-270 degrees
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inx
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lda cosine_table,Y
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dey
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bpl gensin_loop2
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;---------------------------------------
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; raycaster
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;---------------------------------------
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loop_main:
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; cast 40 rays for each screen column
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; starting with rightmost one
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; Y is used as global column index
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; throughout the rest of the program
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ldy #39
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loop_ray:
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; determine current ray's direction
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; by taking player's current direction
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; and fov into account
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; fov is 40 b-rads out of 256 b-rads
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tya
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clc
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adc HEADING
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;sec
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sbc #19+1 ; half of the fov (+1 because of sec)
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tax
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; get sin/cos values accordingly
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; and copy player position to current ray position
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; distance is reset on return from this call
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jsr getsincos_copyplr2ray
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; reset line row before each column gets drawn
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; (needed in vertical line section)
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; X is 0 here?
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stx DISTANCEL
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stx DISTANCE
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loop_dist:
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; step along current ray's path and find distance
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clc
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lda DISTANCEL
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adc #$80
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sta DISTANCEL
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bcc nod
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inc DISTANCE
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nod:
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; limit distance when it is needed in larger maps
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; or open (wrapped) maps
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; max distance = $29
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lda DISTANCE
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cmp #$29
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bcs skip_dist
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; max distance = $40 (make sure ar is always 0 here)
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; bit DISTANCE
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; bvs skip_dist
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; max DISTANCE = $80
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; lda DISTANCE
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; bmi skip_dist
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jsr addsteptopos
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; on return from last call, A is cell (block) value
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; A == 0 means empty cell, so continue tracing
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beq loop_dist
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skip_dist:
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; now A contains the value in reached map position
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; (or last cell value fetched if max distance is reached)
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; use A or X to colorize the block
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; and #$07
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; ora #$03
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sta COLORS+1
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; find out visible block height
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; according to distance
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ldx #$ff
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; calculate visible block height through simple division
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lda #0
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sta HEIGHT
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sta HEIGHTL
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height_loop:
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inx
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lda HEIGHTL
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adc DISTANCEL
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sta HEIGHTL
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lda HEIGHT
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adc DISTANCE
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sta HEIGHT
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cmp #<blocksize
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bcc height_loop
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;dex
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; lda #<blocksize
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;loop_div:
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; inx
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; ; sec
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; sbc DISTANCE
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; bcs loop_div
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; X = half of visible block height
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txa
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;---------------------------------------
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; vertical line
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;---------------------------------------
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; Y = x position (screen column)
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; A = half height (zero height is ok)
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cmp #24 ; height > 24?
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bcc vline_validheight
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lda #23 ; make sure max height = 24
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vline_validheight:
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asl ; calculate full height
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sta WALL_HEIGHT ; store for looping below
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eor #$ff ; subtract full height from screen height
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; sec ; (48 rows)
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adc #48+1 ; +1 because of sec
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lsr ; sky/floor heights are equal to each other
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sta FLOOR_SKY_HEIGHT
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; loop through 3 sections of one screen column
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; i.e. sky - wall - floor
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vline_loop:
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;==========
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; vline sky, 0 to FLOOR_SKY_HEIGHT
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; load color
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;lda #$77 ; sky blue
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lda #$00 ; sky black
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sta COLOR
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lda FLOOR_SKY_HEIGHT
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sta V2
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lda #0
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jsr VLINE ; VLINE A,$2D at Y (Y preserved, A=V2)
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;=================
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; vline wall, FLOOR_SKY_HEIGHT to FLOOR_SKY_HEIGHT+WALL_HEIGHT
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ldx COLORS+1
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stx COLOR
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; A already FLOOR_SKY_HEIGHT
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clc
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adc WALL_HEIGHT
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sta V2
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lda FLOOR_SKY_HEIGHT
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jsr VLINE ; VLINE A,$2D at Y
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;=============
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; vline floor, WALL_HEIGHT+FLOOR_SKY_HEIGHT to 47
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ldx #$88
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stx COLOR
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; A already WALL_HEIGHT+FLOOR_SKY_HEIGHT
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ldx #47
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stx V2
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jsr VLINE ; VLINE A,$2D at Y
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;---------------------------------------
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; advance to next ray/column
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dey
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bpl loop_ray
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;---------------------------------------
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; user input
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;---------------------------------------
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; common preparation code to set up sin/cos and
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; to copy player position to ray position to trace movement
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; direction to determine if player hits a block
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; in case player actually tries to move forward or backwards
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ldx HEADING
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jsr getsincos_copyplr2ray
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; get joystick 2 status (lowest 4 bits)
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; and check each bit to determine action
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lda KEYPRESS
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beq done_user_input
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cmp #'W'+$80
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bne skip_j1
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; try to move forward
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pha
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jsr stepandcopy
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pla
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skip_j1:
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cmp #'S'+$80
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bne skip_j2
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; try to move backward
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pha
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jsr invertstepandcopy
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pla
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skip_j2:
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cmp #'A'+$80
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bne skip_j3
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; turn right
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dec HEADING
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dec HEADING
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skip_j3:
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cmp #'D'+$80
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bne done_user_input
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; turn left
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inc HEADING
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inc HEADING
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done_user_input:
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bit KEYRESET ; clear keyboard buffer
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; absolute jump, as carry is always 0 here
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jmp loop_main
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;---------------------------------------
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; ray tracing subroutines
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;---------------------------------------
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; heart of tracing, very slow, because of looping
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; for x and y components and also because of
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; brute force approach
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addsteptopos:
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ldx #$0
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stx NEWLOC
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ldx #$02
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loop_stepadd:
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lda STEPX,X ; & y
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ora #$7f ; sign extend 8 bit step value to 16 bit
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bmi was_neg ; was negative
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lda #$00
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was_neg:
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pha
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;clc
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lda STEPX,X ; & y
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adc RAYPOSX,X ; & y
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sta RAYPOSX,X ; & y
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pla
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php
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bcc blah ; no carry
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cpx #2
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bne blah
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stx NEWLOC
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blah:
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plp
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adc RAYPOSXH,X ; & y
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sta RAYPOSXH,X ; & y
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dex
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dex
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bpl loop_stepadd
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; A = RAYPOSXH
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; calculate index to look up the map cell
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; the map area is 8x8 bytes
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; + instead of the usual y * 8 + x
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; x * 8 + y done here, to save some bytes
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; (just causing a flip of the map as a side effect)
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and RAYPOSYH ; sierpinski
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and #$f0
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beq step_exit
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lda #$CC
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; jmp blargh
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;make_zero:
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; lda #$00
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; beq step_exit
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;blargh:
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ldx NEWLOC
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cpx #2
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bne step_exit
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sec
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sbc #$88
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step_exit:
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rts
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;---------------------------------------
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; getsincos_copyplr2ray
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;---------------------------------------
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getsincos_copyplr2ray:
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txa
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lsr
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lsr
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tax
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lda sin_t,X ; sin(x), 0..16
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cmp #$80
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ror
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sta STEPX
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lda sin_t+$10,X ; cos(x)
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cmp #$80
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ror
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sta STEPY
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; copy player position to ray position for a start
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; through the basic rom
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; copy 4 bytes, from 69,6A,6B,6C to 61,62,63,64
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copyplr2ray:
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ldx #$04
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copyloop:
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lda $68,X
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sta $60,X
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dex
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bne copyloop
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rts
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;======================================
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; invert step and copy
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;======================================
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invertstepandcopy:
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; invert step variables for backward motion
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invertstepx: ; from BFB8 in C64 ROM
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lda $66
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eor #$ff
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sta $66
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invertstepy:
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lda STEPY
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eor #$ff
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sta STEPY
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;=======================================
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; stepandcopy
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;=======================================
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stepandcopy:
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; see if player can move to the direction desired
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jsr addsteptopos
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bne step_exit ; no, return without doing anything
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; yes, move player by
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; copying ray position to player position
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copyray2plr:
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; Copy 61,62,63,64 to 69,6A,6B,6C
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ldx #$4
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r2_loop:
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lda $60,X
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sta $68,X
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dex
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bne r2_loop
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rts
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;---------------------------------------
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; data
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;---------------------------------------
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; number of sin additions (backwards)
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sincount_t:
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; .byte 6,14,19,25
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;---------------------------------------
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